Inhibitors of human immunodeficiency virus (HIV) protease have been approved for use in the treatment of HIV infection for several years. A particularly effective HIV protease inhibitor is (2S,3S,5S)-5-(N-(N-((N-methyl-N-((2-isopropyl-4-thiazolyl)-methyl) amino)carbonyl)-L-valinyl)amino-2-(N-((5-thiazolyl)methoxy-carbonyl)-amino)-1,6-diphenyl-3-hydroxyhexane (ritonavir), which is marketed as NORVIR®. Ritonavir is known to have utility for the inhibition of HIV protease, the inhibition of HIV infection, and the enhancement of the pharmacokinetics of compounds which are metabolized by cytochrome P450 monooxygenase. Ritonavir is particularly effective for the inhibition of HIV infection when used alone or in combination with one or more reverse transcriptase inhibitors and/or one or more other HIV protease inhibitors.
HIV protease inhibiting compounds typically are characterized by having poor oral bioavailability, and there is a continuing need for the development of improved oral dosage forms for HIV protease inhibitors having suitable oral bioavailability, stability, and side effects profiles.
Ritonavir and processes for its preparation are disclosed in U.S. Pat. No. 5,541,206, issued Jul. 30, 1996, the disclosure of which is herein incorporated by reference. This patent discloses processes for preparing ritonavir which produce a crystalline polymorph of ritonavir, known as crystalline Form I.
Another process for the preparation of ritonavir is disclosed in U.S. Pat. No. 5,567,823, issued Oct. 22, 1996, the disclosure of which is herein incorporated by reference. The process disclosed in this patent also produces ritonavir as crystalline Form I.
Pharmaceutical compositions comprising ritonavir or a pharmaceutically acceptable salt thereof are disclosed in U.S. Pat. No. 5,541,206, issued Jul. 30, 1996; U.S. Pat. No. 5,484,801, issued Jan. 16, 1996; U.S. Pat. No. 5,725,878, issued Mar. 10, 1998; and U.S. Pat. No. 5,559,158, issued Sep. 24, 1996 and in International Application No. WO98/22106, published May 28, 1998 (corresponding to U.S. Ser. No. 08/966,495, filed Nov. 7, 1997, now U.S. Pat. No. 6,232,333), the disclosures of all of which are herein incorporated by reference.
The use of ritonavir to inhibit an HIV infection is disclosed in U.S. Pat. No. 5,541,206, issued Jul. 30, 1996. The use of ritonavir in combination with one or more reverse transcriptase inhibitors to inhibit an HIV infection is disclosed in U.S. Pat. No. 5,635,523, issued Jun. 3, 1997. The use of ritonavir in combination with one or more HIV protease inhibitors to inhibit an HIV infection is disclosed in U.S. Pat. No. 5,674,882, issued Oct. 7, 1997. The use of ritonavir to enhance the pharmacokinetics of compounds metabolized by cytochrome P450 monooxygenase is disclosed in WO 97/01349, published Jan. 16, 1997 (corresponding to U.S. Ser. No. 08/687,774, filed Jun. 26, 1996, now U.S. Pat. No. 6,037,157). The disclosures of all of these patents and patent applications are herein incorporated by reference.
Examples of HIV protease inhibiting compounds include:    N-(2(R)-hydroxy-1(S)-indanyl)-2(R)-phenylmethyl-4(S)-hydroxy-5-(1-(4-(3-pyridylmethyl)-2(S)-N′-(t-butylcarboxamido)-piperazinyl))-pent aneamide (for example, indinavir) and related compounds, disclosed in European Patent Application No. EP 541168, published May 12, 1993, and U.S. Pat. No. 5,413,999, issued May 9, 1995, both of which are herein incorporated by reference;    N-tert-butyl-decahydro-2-[2(R)-hydroxy-4-phenyl-3(S)-[[N-(2-qu inolylcarbonyl)-L-asparaginyl]amino]butyl]-(4aS,8aS)-isoquinoline-3(S)-carboxamide (for example, saquinavir) and related compounds, disclosed in U.S. Pat. No. 5,196,438, issued Mar. 23, 1993, which is incorporated herein by reference;    5 (S)-Boc-amino-4(S)-hydroxy-6-phenyl-2(R)-phenylmethylhexanoyl -(L)-Val-(L)-Phe-morpholin-4-ylamide and related compounds, disclosed in European Patent Application No. EP532466, published Mar. 17, 1993, which is incorporated herein by reference;    1-Naphthoxyacetyl-beta-methylthio-Ala-(2S,3S) -3-amino-2-hydroxy-4-butanoyl 1,3-thiazolidine-4-t-butylamide (for example, 1-Naphthoxyacetyl-Mta-(2S,3S)-AHPBA-Thz-NH-tBu), 5-isoquinolinoxyacetyl-beta-˜nethylthio-Ala-(2S,3S)-3-amino-2-hydroxy-4-butanoyl-1,3-thiazolidine-4-t-butylamide, and related compounds, disclosed in European Patent Application No. EP490667, published Jun. 17, 1992 and Chem. Pharm. Bull. 40 (8) 2251 (1992), which are both incorporated herein by reference;    [1 S-[1 R-(R-),2S*])-N1 [3-[[[(1,1-dimethylethyl)amino]carbonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl)propyl]-2-[(2-quinolinylcarbonyl)amino]-butanediamide (for example, SC-52151) and related compounds, disclosed in PCT Patent Application No. WO92/08701, published May 29, 1992 and PCT Patent Application No. WO93/23368, published Nov. 25, 1993, both of which are herein incorporated by reference;
(for example, VX-478) and related compounds, disclosed in PCT Patent Application No. WO 94/05639, published Mar. 17, 1994, which is incorporated herein by reference;
(for example, DMP-323) or
(for example, DMP-450) and related compounds, disclosed in PCT Patent Application No. WO 93/07128, published Apr. 15, 1993, which is incorporated herein by reference;
(for example, AG1343, (nelfinavir)), disclosed in PCT Patent Application No. WO 95/09843, published Apr. 13, 1995 and U.S. Pat. No. 5,484,926, issued Jan. 16, 1996, which are both incorporated herein by reference;
(for example, BMS 186,318) disclosed in European Patent Application No. EP580402, published Jan. 26, 1994, which is incorporated herein by reference;
(for example, SC-55389a) and related compounds disclosed in PCT Patent Application No. WO 9506061, published Mar. 2, 1995, which is incorporated herein by reference and at 2nd National Conference on Human Retroviruses and Related Infections, (Washington, D.C., Jan. 29–Feb. 2, 1995), Session 88; and
(for example, BILA 1096 BS) and related compounds disclosed in European Patent Application No. EP560268, published Sep. 15, 1993, which is incorporated herein by reference; and
(for example, U-140690 (tipranavir)) and related compounds disclosed in PCT Patent Application No. WO 9530670, published Nov. 16, 1995, and U.S. Pat. No. 5,852,195, issued Dec. 22, 1998, the disclosures of both of which are herein incorporated by reference; or a pharmaceutically acceptable salt of any of the above.
Another example of an HIV protease inhibiting compound includes a compound of formula I:
or a pharmaceutically acceptable salt thereof, disclosed in PCT Patent Application No. WO 94/14436, published Jul. 7, 1994, and U.S. Pat. No. 5,541,206, issued Jul. 30, 1996, the disclosures of both of which are herein incorporated by reference.
The compounds of formula I are useful to inhibit HIV infections and, thus, are useful for the treatment of AIDS. Another example of an HIV protease inhibiting compound is a compound of formula II:
and related compounds, or a pharmaceutically-acceptable salt thereof, as disclosed in U.S. patent application Ser. No. 08/572,226, filed Dec. 13, 1996 now abandoned and U.S. patent application Ser. No. 08/753,201, filed Nov. 21, 1996 now U.S. Pat. No. 5,914,332, and International Patent Application No. WO 97/21685, published Jun. 19, 1997, the disclosures of which are herein incorporated by reference. A preferred compound of formula II is known as ABT-378 and has a chemical name of (2S,3S,5S)-2-(2,6-dimethylphenoxyacetyl)-amino-3-hydroxy-5-(2S-(1-tetrahydropyrimid-2-onyl)-3-methyl-butanoyl)amino-1,6-diphenylhexane, or a pharmaceutically-acceptable salt thereof. The preparation of this compound is disclosed in U.S. Pat. No. 5,914,332, issued Jun. 22, 1999, the disclosure of which is herein incorporated by reference.
Solubility is an important factor in the formulation of HIV protease inhibiting compounds. Compounds of formula I typically have an aqueous solubility of approximately 6 micrograms per milliliter at pH>2. This is considered to be extremely poor aqueous solubility and, therefore, a compound of formula I in the free base form would be expected to provide very low oral bioavailability. In fact, the free base form of a compound of formula I, administered as an unformulated solid in a capsule dosage form, is characterized by a bioavailability of less than 2% following a 5 mg/kg oral dose in dogs.
Acid addition salts of a compound of formula I (for example, bishydrochloride, bistosylate, bis-methane sulfonate and the like) have aqueous solubilities of <0.1 milligrams/milliliter. This is only a slight improvement over the solubility of the free base. This low aqueous solubility would not make practical the administration of therapeutic amounts of an acid addition salt of a compound of formula I as an aqueous solution. Furthermore, in view of this low aqueous solubility, it is not surprising that the bis-tosylate of a compound of formula I, administered as an unformulated solid in a capsule dosage form, is characterized by a bioavailability of less than 2% following a 5 mg/kg oral dose in dogs.
In order to have a suitable oral dosage form of a compound of formula I, the oral bioavailability of a compound of formula I should be at least 20%. Preferably, the oral bioavailability of a compound of formula I from the dosage form should be greater than about 40% and, more preferably, greater than about 50%.
One measure of the potential usefulness of an oral dosage form of a pharmaceutical agent is the bioavailability observed after oral administration of the dosage form. Various factors can affect the bioavailability of a drug when administered orally. These factors include aqueous solubility, drug absorption, dosage strength and first pass effect. Aqueous solubility is one of the most important of these factors. When a drug has poor aqueous solubility, attempts are often made to identify salts or other derivatives of the drug which have improved aqueous solubility. When a salt or other derivative of the drug is identified which has good aqueous solubility, it is generally accepted that an aqueous solution formulation of this salt or derivative will provide the optimum oral bioavailability. The bioavailability of the oral solution formulation of a drug is then generally used as the standard bioavailability against which other oral dosage forms can be measured.
For a variety of reasons, such as patient compliance and taste masking, a solid dosage form, such as capsules, is usually preferred over a liquid dosage form. However, oral solid dosage forms, such as a tablet or a powder, and the like, of a drug generally provide a lower bioavailability than oral solutions of the drug. One goal of the development of a suitable capsule dosage form is to obtain a bioavailability of the drug that is as close as possible to the bioavailability demonstrated by the oral solution formulation of the drug.
While some drugs would be expected to have good solubility in organic solvents, it would not necessarily follow that oral administration of such a solution would give good bioavailability for the drug. It has been found that a compound of formula I has good solubility in pharmaceutically acceptable organic solvents and that the solubility in such solvents is enhanced in the presence of a pharmaceutically acceptable long chain fatty acid. Administration of the solution as an encapsulated dosage form (soft elastic capsules or hard gelatin capsules) provides an oral bioavailability of as high as about 60% or more.
Thus, it would be an important contribution to the art to provide an improved pharmaceutical formulation comprising at least one solubilized HIV protease inhibiting compound having enhanced solubility properties.